Welding system



Dec. 9, 1941. D. B. scoTT 2,265,930l WELDING SYSTEM Filed July 12, 1940Patented Dec. 9, 1941 WELDING SYSTEM Donald B. Scott, West Allis, Wis.,assignor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis., acorporation of Delaware Application July 12, 1940, Serial N0. 345,032

(Cl. 21B-8) 12 Claims.

This invention relates in general to welding systems and moreparticularly to an arc welding system operable efficiently within a widerange of current intensities including such low currents as to permitwelding of thin sheets of ferrous and other metallic materials.

Electric arc welding machines are generally provided with adjustingmeans permitting to select the desired value of welding current Withinthe operating range of the machine. The range of regulation obtained is,however, restricted, the ratio between the highest and the lowest stableWelding current given by any machine usually being less than ten to one.The lowest currents obtainable are usually of the order of twenty tothirty amperes, but such currents frequently cannot be used because ofthe lack of stability of the arc. Static welding systems utilizingtapped transformers or reactors likewise are-limited to a relativelynarrow range of regulation for reasons of cost and they also fail tosupply table welding currents below twenty amperes.

The above disadvantages may be obviated by utilizing an arrangement inwhich alternating current regulated by means of adjustable reactors isrectified by a system comprising a transformer and a plurality ofelectric valves. To obtain stable welding current of low values thetransformer core may be caused to become saturated, the transformer thendrawing an increased magnetizing current causing the value of thewelding current to decrease beyond the range determined by thecharacteristics of the reactors. The arc is then so stable that it maybe lengthened to a point where the arc fails to transfer metal betweenthe welding electrodes.

It is therefore an object of the present invention to provide a weldingsystem producing stable welding currents of less than twenty amperes.

Another object of the present invention is to provide a welding systemcomprising common regulating means for obtaining two ranges ofvregulation.

Another object of the present invention is to provide a welding systemproducing stable welding current continuously variable between values ina ratio greater than ten to one.

Another object of the present invention is to provide an arc weldingsystem in which the arc may be lengthened sufficiently to precludetransfer of metal between the electrodes by the arc.

Objects and advantages other than those above set forth will be apparentfrom the following description when read in connection with theaccompanying drawing, in which:

Fig. 1 diagrammatically illustrates one embodiment of the presentinvention adapted to convert three phase alternating current into directwelding current;

Fig. 2 is a graph showing two of the arc characteristics obtained bymeans of the embodiment illustrated in Fig. l when all valves of thesystem are utilized; and

Fig. 3 is a graph showing two of the arc characteristics obtained whenone-half of the valves of the system are utilized.

Referring more particularly to the drawing by characters of reference,reference numeral 6 designates a three phase low voltage alternatingcurrent supply circuit such as are usually available for the supply ofcurrent to welding systems. Welding current is to be supplied to a pairof Welding electrodes l, 8 of which electrode 'I is assumed to be thework to be welded. Electrode 8 is a rod supplying the metal for theweld, preferably a coated rod. The electrodes are connected with circuit6 through means for converting current from the circuit 6 into directcurrent and for supplying the direct current to the electrodes, suchmeans comprising a plurality of inductive reactors 9, a suitable threephase transformer aggregate I0 and two groups of electric valves Il, I2.

Each reactor 9 comprises a three legged core I3 of which the middle legcarries a saturating winding I4 for impressing a unidirectionalmagnetomotive force on the core to control the magnetization thereof.The inductive winding I6 of the reactor is divided into two portionsarranged on the outer legs of the core and connected either in series orin parallel to cause the Winding to present the same reactance to bothhalf cycles of the ow of current therethrough. Transformers IIJ comprisea plurality of magnetically independent cores I1 preferably presenting auniform cross section to the flow of magnetic flux therethrough. Eachcore I'I is wound with one of the portions of a primary winding I9defining a phase thereof and with two secondary winding portions 2U, 2Idefining two opposite phases. The phase portions of winding I9 areconnected in star and the terminals thereof are severally connected withthe conductors of circuit 6 through windings IG of reactors 9. Theneutral point of winding I9 is not connected with circuit 6.

The phase portions of winding 20 are connected in star to deiine aneutral point connected with one of electrodes 1, 8 through one of theblades of a double pole reversing switch 22. The terminals of winding 20are severally con- 4are similar to valves II.

nected with thel cathodes of valves II, which are preferably of the hotcathode mercury vapor type. The anodes of valves II are connected withthe other one of electrodes 1, 8 through the second blade of switch 22.The phase portions of winding 2I are connected in star to define aneutral point connected with the neutral point of winding 20. Theterminals of winding 2I are severally connected with the cathodes ofvalves I2, which Winding 2l may be operatively disconnected fromelectrodes 1, 8 by means of a single pole switch 23 inserted in thecommon connection between switch 22 and the anodes of valves I2 tothereby render Winding 2| inoperative. The cathode filaments of valvesII, I2 are energized from any suitable sources such as secondarywindings of a" transformer 24 connected with circuit 6. Transformer 24may also be provided with an additional secondary winding 28 supplyingcurrent to a voltage divider 21 through a suitable rectifying device 28.Windings I4 are connected in series between a terminal and the tap ofvoltage divider 21 to vary the degree of magnetization of cores I3.

The dimensions ofthe diierent elements of the system above describedvary with the magnitude of the welding current to be obtained, but suchdimensions should be correlated and maintained within predeterminedlimits to obtain the desired results from the system. For example, letit be assumedthat a range oi welding current of five to seventy-liveamperes be desired. If coated electrodes are used. the arc voltage maybe assumed to be twenty-five volts. If circuit 6 operates at a voltageof 230 volts, at no load each phase portion of winding I9 will receive amaximum voltage of substantially 133 volts. 'I'he windings oftransformer I0 should be so wound that at no load each phase portion ofwindings 20, 2I has induced therein a voltage of substantiallysixtyvolts. The no load maximum flux density in cores I1 should be oftheorder of 11,500 gausses and the no load magnetizing current of thetransformers is of the order of 1 ampere. Reactors 8 have preferably areactance of substantially ten ohms, which may gradually be reduced toone ohm by suitable adjustin the sequence in which the differentcathodes reach the lowest negative potential. The differment of the flowof current through windings I4.

In operation, circuit 8 being energized from a suitable source (notshown), switch 22 is left in the position shown or is reversed dependingon the nature of the coating of electrode 8. When welding currentswithin a range reaching relatively high intensities are desired, switch23 is closed to operatively connect valves I2 and winding 2.I with theelectrodes. 'I'he phase voltages of circuit 6 are impressed on thedifferent portions of Winding I9 through windings I6, inducing a sixphase system of voltages in the phase portions of windings 20, 2I. Thelatter voltages are sequentially impressed on electrodes 1, 8 throughvalves Il, I2.

The welding arc is ignited by momentarily engaging electrode 8 withelectrode 1 and is thereafter maintained by withdrawing electrode 8 to adistance from electrode 1. The anodes of valves II, I2 are maintained ata common potential by the connection therebetween. The cathodes of thedifferent valves, however, are sequentially brought to a negativepotential with respect to thecommon anode potential by the voltages ofassociated portions of windings 20, 2 I. 'I'he cathode momentarilyhaving the most negative potential carries current and the flow ofcurrent is transferred from cathode to cathode ent cathode currentscombine at the neutral point of windings 20, 2I to form a flow ofunidirectional current supplied `to electrodes 1, 8 to maintain the arcltherebetween.

Although the ow of current through the different valves is initiated insequence, the periods of conduction of the valves overlap to an extentdepending on the value of the welding current and on the reactance ofreactors 9. The voltage between electrodes 1, 8 is equal to a voltageproportional to the induced voltage of windings 28, 2I less the arc dropin valves II, I2, which amounts to approximately '1 volts. The voltageof windings 20, 2l, however, varies continuously from no load to normalload conditions obtained when the electrodes carry normal weldingcurrent. The relation between the larc current and the voltage acrossthe arc when the arc length is increased from normal to a length causingits extinction is represented by a. curve such as curve 29 of Fig. 2when the saturating windings I4 are not supplied with current fromvoltage divider 21. During such operation valves II, I2 operatewithoutvmaterial overlap and current therefore flows generallythroughonly one of the valves. The lowest point of the curve corresponds tonor- -mal welding conditions at twenty-five volts arc voltage with thelowest welding current obtainable when all the valves are utilized.

If the tap of Voltage divider 21 is moved to the right hand terminal ofthe voltage divider, windings I4 receive a maximum rectied current fromwinding 2B through rectifying device 28. The reactance of windings I6 isthereby reduced to a minimum value and the arc current ows under avoltage represented by curve 30 corresponding to a welding current ofmaximum value. With this adjustment of voltage divider 21, if the arccurrent is maintained comparatively low by excessive lengthening of thearc, the dierent valves II, I2 operate in the sequence of the voltagesof winding portions 2D, 2l as with the low current adjustment abovedescribed.

If the arc current is allowed to exceed a predetermined critical value,-the operation of the system becomes somewhatl different from -theabove. Winding 20 and valves II operate as a three phase system in whichthe valves carry current in the sequence of the voltages of theassociated portions of 'winding 28 to supply current to the arc. At thesame time winding 2I and valves I2 operate as another three phase systemin which valves I2 carry current in the sequence of the voltages ofwindingportion 2| independently of winding 20 and of Valves II. Theperiods of operation of valves II overlap those of valves I2, currentowing both through one of the valves II and through one of the valves I2at every instant. When the welding current exceeds the critical load,the rate of change of the arc voltage with the current becomes smaller,causing a knee in the voltage curve at point 3l. Any desired arccharacteristic intermediate those represented by curves 29 and 30 may beobtained by setting the tap of voltage divider 21 at selected pointsintermediate the terminals of the voltage divider.

When current of relatively low intensity is desired, switch 23 is leftopen to render winding 2| and valves I2 inoperative. Each core I1 isthen operatively associated with a primary winding portion and with asecondary winding portion of only one phase. The no load arc voltage isthereby reduced by approximately fifteen percent from the value obtainedduring operation with all the valves. While the now of current througheach portion of winding 20 is unidirectional, the current through theassociated portion of winding I9 is alternating. Each core l1 isaccording- 1y subjected to a residual unidirectional magnetomotive forceequal to the magnetomotive force which would be produced by the flow ofone-third of the welding current through the associated portion ofwinding 20. In addition thereto the cores are also subjected to thealternating magnetization required for inducing operating voltages fromwinding I9 to winding 20.

Cores i1 are so dimensione@ that the maximum magnetization thereofreaches the range of socalled saturation, thereby increasing themagnitude of the magnetizing current required for obtaining thealternating component of magnetization of the cores. The saturation oithe cores and hence the magnetizing current flowing from circuit 6through windings IE and winding IS increase with the welding current butdisproportionally thereto. Windings i6 therefore carry an alternatingcurrent component to be converted into welding current and also analternating component serving to magnetize transformers nl Il. Becauseof the saturation of cores I1 the latter component is of sufficientmagnitude to cause a material voltage drop in winding I6 to therebycontrol the value of the welding current. The welding current may befurther controlled by varying the unidirectional magnetomotive forceimpressed on cores I 3 by windings I4.

Cores Il are preferably so dimensioned that the maximum magnetization ofthe cores is then maintained within the limits of 12,500 to 23,50@gausses regardless of the setting of voltage diobtained by means ofvalves H alone when windvider 21 and of the resulting value of thewelding current. The magnetizing current drawn by transformers l@ fromcircuit B through windings it then reaches 'vmues ranging from the valueof the current supplied from circuit E to be converted into weldingcurrent to twice such. value. As the voltage drop in windings IE resultsfrom the ilow therethrough both of the useful current componentsupplying welding current and of the magnetizing current component, thecurrent limiting effect of the reactors becomes greatly increased overthat obtained during operation with all the valves il, l2. Withoutincrease in the cost of the system it is therefore possible to decreasethe Welding current considerably below the lowest value which could beobtained during operation with all the valves or during operation withonly valves Il without saturation of transformer l0.

The maximum magnetization of cores l1 is designed to reach at least avalue of 12,500 gausses because at lower values the magnetizing currentof the transformers is too low to influence materially the currentlimiting effect of reactors 9. When the magnetizationof the transformersexceeds the value of 23,500 gausses, the

core losses of the transformers become excessive.

The system then becomes impractical because of the cost of the energydissipate'd in such losses and because of the difficulty of removing theheat thereby evolved in the cores. When the transformers Il aremagnetized within the limits specified, opening of switch 23 causes thewelding current to decrease-by substantially one-half of the valuethereof previously obtained by adjustment of voltage divider 21.

Curve l2 in Fig. 3 represents the arc voltage normal arc current has avalue of five amperes. for which an electrode 8 having a diameter of onethirty-second of an inch is required. By saturating reactors 9 currentup to 35 amperes may be obtained for which electrodes up to onesixteenthof an inch in diameter may be utilized. Curve 33 represents the arcvoltage obtained when. reactors t are saturated by a maximum ow ofcurrent through windings it. Arc characteristics intermediate thoserepresented by curves 32 and 23 may be obtained by mutable aojustment ofthe tap or? voltage divider il.

The arc obtained characterized by a 'high degree of stability regardlessoi the degree of saturation of reactors Q. The arc may be used forsuccessfully transferring weld-forming metal from the rod electrode tothe worls when the are length is maintained within a predetermined rangeof approximately one-sixteenth of an inch to three thirty-seconds of aninch for currents ranging from five to thirty-:live amperes. With thesame adjustment of reactors 9 the arc may be lengthened within anotherpredetermined range of approximately three thirty-seconds of an inch toone-eighth of an inch without being interrupted. Because of thereduction of the current corresponding to the increase in the arcvoltage and because of the dissipation of the heat of the arc through alarger arc volume, the arc is then unable to transfer metal from the rodelectrode to the work. Some of the electrode metal may, however, slowlymelt to form occasional drops which are separated from the rod by gra'ity. At higher values of current the arc length may increase up toone-eighth of an inch during transfer of metal to form a weld and up toonehalf inch during operation With-cut transfer of metal.

The welding current, which is unidirectional., is nevertheless or highlypulsating character as it is produced by a succession of sinusoidal'voltage peaks each extending over electrical olegrees., The well knownmagnetic attraction exertecl on the arc by magnetzable objects adjacentthereto is then also pulsating, and the resulting undesired.displacement of the arc path is great- 1y reduced.

Although-lout one embodiment of the present invention has beenillustrated and described it will he apparent to those skilled in theart that vvarious changes and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

It is claimed and desired to secure by Letters Patent:

l. A welding system comprising welding electrodes, an alternatingcurrent supply circuit, means for converting current from said circuitinto direct current and for supplying said direct current to saidelectrodes, said means comprising electric valve means and transformermeans provided with associated cores and windings, inductance meansconnecting said transformer means with said circuit, and meanscomprising the dimensioning of said cores and the arrangement of saidwindings on said cores for subjecting said cores to a unidirectionalmagnetomotive force component causing -the magnetization of said .coresto reach saturation, thereby increasing the ow of current from saidcircuit to said transformer means through said inductance means tocontrol the value of the Welding current.

2. A welding system comprising welding electrodes, an alternatingcurrent supply circuit, means for converting current from said circuitinto direct current and for supplying said direct current to saidelectrodes, said means comprising electric valve means and transformermeans provided with associated cores and windings, inductance meansconnecting said transformer means with said circuit, and meanscomprising the dimensioning of said cores and the arrangement of saidwindings on said cores for causing said transformer means to draw amagnetizing current component greater than the current componentsupplied from said alternating current circuit to be converted into saiddirect current to thereby increase the ow of current from said circuitto said transformer through said inductance means to control the valueof the welding current.

3. A welding system comprising welding electrodes, an alternatingcurrent supply circuit, means for converting current from said circuitinto direct current and for supplying said direct current to saidelectrodes, said means comprising electric value means and transformermeans provided with associated cores and windings, inductance meansconnecting said transformer means with said circuit, and meanscomprising the dimensioning of said cores and the arrangement of saidwindings on said cores for causing the degree of magnetization of saidcores and the magnetizing current of said transformer means to increasewith the magnitude of said direct current.

4. A welding system comprising welding electrodes, a polyphasealternating current supply circuit, means for converting current fromsaid circuit into direct current and for supplying the direct current tosaid electrodes, said means comprising -electric valve means andtransformer means provided with Star connected primary and secondarywindings and with a plurality of magnetically independent cores, each ofsaid cores being associated with primary and secondary vvindings of onlyone phase for subjecting said cores to a unidirectional magnetomotiveforce component causing the magnetization of said cores to reachsaturation, and inductance means connecting said primary winding withsaid alternating current circuit to control the value of the weldingcurrent in dependence upon the degree of saturation of said cores.

5. A welding system comprising welding electrodes, a polyphasealternating current supply circuit, means for converting current fromsaid circuit into direct current and for supplying the direct current tosaid electrodes, said means comprising electric valve means andtransformer means provided with a star connected primary winding, with arst star connected secondary winding, with a second star connectedsecondary winding and with a plurality of cores, each of said coresbeing associated with a portion of said primary winding defining onephase thereof and with a portion of said rst Secondary winding and aportion of said second secondary winding defining two opposite phases,and means for controlling said direct current comprising means forrendering inoperative said second secondary winding.

6. A welding system comprising welding electrodes, a polyphasealternating current supply circuit, means for converting current fromsaid circuit into direct current and for supplying the direct current tosaid electrodes, said means comprising electric valve means andtransformer means provided with a star connected primary winding, with aiirst star connected secondary winding, with a. second star connectedsecondary winding and with a plurality of cores, eachof said cores beingassociated with a portion of said primary winding defining one phasethereof and with a portion of said rst secondary winding and a portionof said second secondary winding defining two opposite phases,inductance means connecting said primary winding with said alternatingcurrent circuit, and means for controlling the voltage drop in saidinductance means to regulate the magnitude of said direct currentcomprising means for rendering inoperative said second secondary windingto cause said circuit to supply additional magnetizing current to saidprimary winding through said inductance means.

7. A welding systemA comprising welding electrodes, a polyphasealternating current supply circuit, means for convertingcurrent fromsaid circuit into direct current and for supplying the direct current tosaid electrodes, said means comprising electric valve means andtransformer means provided with a star connected primary winding, with arst star connected secondary winding, with a second star connectedsecondary winding and with a plurality of cores, each of said coresbeing associated with a portion of said primary winding defining onephase thereof and with a portion of said first secondary winding and aportion of said second secondary winding defining two opposite phases,inductance means connecting said primary winding with said alternatingcurrent circuit, and means for controlling the voltage drop in saidinductance means to regulate the magnitude of said direct currentcomprising means for varying the inductance of said inductance means andmeans for rendering inoperative said second secondary winding to causesaid circuit to supply additional magnetizing current to said primarywinding through said inductance means.

8. A welding system comprising welding electrodes, a polyphasealternating current supplyv netically independent cores, each of saidcores being associated with primary and secondary windings of only onephase, means comprising the dimensioning of said cores for causing themagnetization of said cores to become dissymmetrical and to reach amaximum value comprised between 12,500 and 23,500 gausses to increasethe magnetizing current of said transformer, and inductance meansconnecting said primary winding with said alternating current circuit tocontrol the value of the welding current in dependence upon the value ofsaid magnetizing current.

9. A welding system comprising a source of alternating current, weldingelectrodes, means for connecting said electrodes in circuit with saidsource to produce an arc carrying a welding current between saidelectrodes, and means for causing said arc to transfer metal betweensaid electrodes when said arc is of a length within a predeterminedrange and for causing said arc to fail to transfer metal between saidelectrodes 5 when said arc is of a length within another premeegaandetermined range, the last said means comprising means inserted in theconnections between said circuit and said electrodes for convertingalternating current from said circuit into direct current to be suppliedto said electrodes.

10. A welding system comprising a source of alternating current, weldingelectrodes, and means connecting said electrodes in circuit with saidsource operable for producing an arc carrying a welding current betweensaid electrodes for causing said arc to transfer metal between saidelectrodes when said arc is of a length within a predetermined range andfor causing said arc to fail to transfer metal between said electrodeswhensaid arc is oi a length within another predetermined range. A

ll. A welding system comprising a source of alternating current, weldingelectrodes, means for connecting said electrodes in circuit with saidsource to produce an arc carrying a welding current between saidelectrodes, and means for causing said arc to transfer metal betweensaid electrodes when said arc is of a length within a predeterminedrange and ior causing said arc to fail to transfer metal between saidelectrodes when said arc is of a length within another predeterminedrange, the last said means comprising inductance means, transformermeans and electric valve means inserted in the connections between saidcircuit and said electrodes for converting alternating current from saidcircuit into direct current to be supplied to said electrodes.

12. The method of welding comprising passing an alternating currentcomponent through a reactor winding, convertingthe current componentinto welding current, passing the welding current through weldingelectrodes, controlling the magnetization of the reactor byimpressing onthe reactor core a unidirectional magneto- -motive force, and furthercontrolling the magnetization of the reactor by passing through thereactor winding another alternating current increasingdisproportionately to the welding current.

DONALD B. SCOTT.

A CERTIFICATE OF CORRECTION. Patent No. 2,26,95o. December- 9, 19in.

1'* DONALD B. SCOTT.

It is hereby certified thatl error 'appears in the printed specificationof the above numbered patent requiring correction as follows: Page l1.,first column, line 2'?, claim 5, for "Value" read valve-; and that thesaid Let. ters Patent shouldl be read with this correction therein thatthe same may conform to the record of y the case in the Patent Office.

Signed and sealed this 27th day of January; A. D. 19M..

. Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

CERTIFICATE CE CORRECTION. Patent No. 2,26,95o. December 9, 19in.'

DONALD B. SCOITT.

It is hereby certified that' error appears in the printed specificationof the above numbered patent requiring correction as follows: Page h.,first column, line 27, claim 5, for "Value" read valve; and that thesaid Let-j ters Patent should. be read with this correction therein thatthe same may conform to the record of I the case in the Patent Office.

signed and sealed this 27th day of January', A. D. 19m.

. Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

